Ethernet physical layer device using time division duplex

ABSTRACT

An Ethernet physical layer device using time division duplex. A time division duplex frame can be defined with uplink and downlink transmission periods. These defined uplink and downlink transmission periods can be adjusted based on bandwidth and latency considerations on the network link.

This application claims priority to provisional patent application No.61/531,184, filed Sep. 6, 2011, which is incorporated by referenceherein, in its entirety, for all purposes.

BACKGROUND

1. Field of the Invention

The present invention relates generally to Ethernet physical layerdevices and, more particularly, to an Ethernet physical layer deviceusing time division duplex.

2. Introduction

Ethernet is one of the most successful and long lasting designs for datacommunications over wired networks. Ethernet physical layer device (PHY)specifications have evolved significantly. The most recent formats for10 Mbps and 100 Mbps Ethernet PHYs use two pairs of twisted cables,while for 1 Gbps, four pairs of twisted cables are used as specified inthe IEEE 802.3 standard.

In the existing telephony wirings, a single twisted pair is oftenavailable. The wirings may be tapped to provide services at multiplepoints. These tapped wires, which are commonly referred to as “bridgedtaps,” cause strong reflections or echoes affecting signal quality.Coaxial cable networks, which are mainly used for TV signaldistribution, are also single pair. These coaxial cables, which areoften tapped using splitters for multi-room services, cause strongreflections.

What is needed therefore is a mechanism for sending standard Ethernetdata packets over a single-pair cable in a manner that can leverageintegrated mixed signal silicon devices and signal processing techniquesdeveloped for existing Ethernet PHYs.

SUMMARY

An Ethernet physical layer device using time division duplex,substantially as shown in and/or described in connection with at leastone of the figures, as set forth more completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings in which:

FIG. 1 illustrates a transmit block diagram of a time division duplexEthernet PHY.

FIG. 2 illustrates a receive block diagram of a time division duplexEthernet PHY.

FIG. 3 illustrates transmitter activity with symmetric downlink anduplink throughput.

FIG. 4 illustrates transmitter activity with asymmetric downlink anduplink throughput.

FIG. 5 illustrates transmitter activity with low power idle capability.

FIG. 6 illustrates a flowchart of a process of the present invention.

DETAILED DESCRIPTION

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

The IEEE standard Ethernet PHY for a 100 Mbps link uses two pairs ofwires. Extension of this 100 Mbps Ethernet link to a single-pair wirewould include the use of echo-cancellation techniques. Unfortunately,these echo-cancellation techniques are typically limited to cables withcontrolled signal reflections for a receiver with a given dynamic range.As would be appreciated, there are some cabling situations where thereturn signal is not under control. One example of this type of cablingsituation is telephony wiring with bridged taps.

In the present invention, it is recognized that time division duplex(TDD) can be applied to existing Ethernet PHYs, thereby allowingtwo-way, point-to-point communications over a single-pair cable. Here,it is a feature of the present invention that combining TDD withmodulation and signal processing formats native to Ethernet would allowhigh-throughput Ethernet packet transmission that reuses the existingdigital and analog blocks in higher-speed Ethernet PHYs. As would beappreciated, the need for high-resolution, echo-cancellation methods isobviated as this format of communication is immune to large signalreflections.

As will be described in greater detail below, the application of TDD toEthernet PHYs allows for programmable symmetric and asymmetricthroughput in the uplink and the downlink. It also allows for higherpower efficiency and lower radio emission. It should also be noted thatwhile the description below is primarily in the context of two-waycommunications over a single-pair cable, the principles of the presentinvention may be used over multi-pair cables given other inherentbenefits.

FIGS. 1 and 2 show simplified transmit and receive block diagrams,respectively, of a TDD Ethernet PHY. In one embodiment, collision (COL)and carrier sense (CRS) signals can be used at the MII interface tocontrol medium availability, thereby allowing standard half-duplexoperation. While this mechanism may work well in many cases, it may notprovide full bandwidth utilization of the system and could result inincreased latency. It should be noted that with half-duplex connectionto the MAC, the use of FIFO buffers are not necessary, although they canimprove the link throughput.

In the alternative embodiment illustrated in FIGS. 1 and 2, FIFO buffers110, 120 used at the MII interface has CLK2 faster than CLK1. If CLK2 isfast enough and the FIFO buffer 110, 120 is properly sized, then thechannel is always available at the MAC interface, thereby allowing forfull-duplex operation.

With TDD, the medium is shared between the uplink and the downlink. FIG.3 illustrates the timing diagram for a system with symmetric downlinkand uplink data rate. As illustrated, the TX_ON signal generated by acontroller shows the different time periods when data is transmitted onthe medium at the master or slave side. It should be noted that while aTDD system need not require master and slave assignments, those masterand slave assignments can help with initial training and loop timing.

In the present invention, while a signal is transmitted and during aninter-burst gap (IBG) period 300, the local receiver can be isolatedfrom the line to avoid corruption of the receiver DSP state by echoes ofthe transmitter. The receiver DSP block 220 can be trained only duringthe time it is receiving data or idle signals from the other side.

FIG. 4 illustrates the TX_ON signal for a system with asymmetricdownlink and uplink data rates. As illustrated, TX_ON signal 410 can beused to define a longer transmission period of the master, while TX_ONsignal 420 can be used to define a relatively shorter transmissionperiod of the slave. By this mechanism, more time may be assigned to themaster or the slave in this case, effectively increasing throughput foreither the downlink or the uplink. The use of asymmetric downlink anduplink data rates can be beneficial to those traffic profiles that arenot symmetric.

For example, a traffic profile represented by a surveillance camera orstreaming video traffic is not symmetrical as the amount of streamingvideo data in one direction would far exceed the amount of control datain the other direction. An application of asymmetric downlink and uplinkdata rates would therefore match the different levels of throughput inthe two directions of transmission.

In one embodiment, the automatic adjustment of downlink and uplink ratescan be used to generate improvements in latency and throughput. Forexample, if the downlink has no data to send, then the channel can bereleased to the uplink although, even though the downlink transmissionperiod may not have completed yet. In this case, most of the bandwidthmay be given to the downlink when downloading and to the uplink whenuploading.

In enabling adaptive downlink and uplink data rates, the transmit timeperiod can be actively tuned for both the uplink and the downlink insuch a way that it provides maximum throughput and maintains latencyrequirements. For example, if the transmit FIFO buffer is empty in onedirection, then control can be given to the other side of the link fortransmission.

In one embodiment, a minimum and a maximum burst time can be used toensure that the receiver DSP can maintain its status and track clock orchannel variations. The maximum burst time can take into account thelatency requirement as well. While the highest throughput can beachieved when the TDD frame is allowed to vary adaptively, in oneembodiment, the TDD frame size can be considered constant while uplinkand downlink transmission time periods are assigned adaptively.

In one embodiment, power efficiency and unwanted radio emissions canalso be improved if no signal is sent during system idle where no datais communicated. FIG. 5 illustrates the TX_ON signal for a system withLow Power Idle (LPI) capability. When there is no data to be sent, theline may be quiet in both directions for a period longer than the IBG asthe LPI capability is leveraged.

In one embodiment, a periodic minimum transmission of data or idlesignal can be considered to ensure that the receiver DSP status ismaintained. It is a feature of the present invention that LPI can beconsidered and combined with symmetric, asymmetric or adaptive bursttime allocations.

As an example system design, consider a standard 100 Mbps MII interfacewhere CLK1 is 25 MHz and data is 4 bits wide. Also assume uplink anddownlink transmission period durations are 220 μsec each and there is anIBG of 10 μsec. If CLK2 is greater than 25*2*(220+10)/220=52.27 MHz andthe FIFO buffer size is greater than 25/2*(10+220+10)=3 KB, then fullduplex connection at the MII interface at the standard 100 Mbps rate canbe achieved.

For the same example above with CLK2 fixed at 52.27 MHz assume that thedownlink transmission period duration is programmed to be 10 timeslarger than the uplink transmission period duration (e.g., 400 μsecversus 40 μsec). This allows for downlink throughput of up to400/(460)*52.27 MHz*4 bits/Hz=182 Mbps and uplink throughput of up to 18Mbps. The clock at the MII interface or CLK1 may be adjusted to allowfor this rate change if the MAC device allows for the intermediate clockspeeds. It is also possible to select a fixed higher rate clock at theMII interface and use flow control to allow for variable and/oradjustable throughput at the downlink and uplink. IEEE standard PAUSEcommands can also be used to provide flow control in this case.

Having described an example application of the principles of the presentinvention, reference is now made to the flowchart of FIG. 6, whichillustrates a process of the present invention. As illustrated, theprocess begins at step 602 where a TDD frame is defined. As noted above,in one embodiment, the TDD frame can be considered as a constant whileuplink and downlink transmission periods vary within the TDD frame. Oncedefined, the TDD frame can describe uplink and downlink transmissionperiods to suit a given traffic profile on a network link. In variousexamples, the uplink and downlink transmission periods can be definedwith equal time periods or unequal time periods.

At step 604, the transmitter in the uplink direction can be giventransmission control based on a TX_ON signal generated by a controllerin a first physical layer device during a first transmit portion of theTDD frame. This TX_ON signal can be generated by the controller inaccordance with the TDD frame structure that was defined. Once the TX_ONsignal indicates completion of the uplink transmission period,transmission control would effectively be given to a second physicallayer device at the other end of the link, where a corresponding TX_ONsignal is generated to indicate that transmission in the down linkdirection can proceed. At step 606, the first physical layer devicewould then receive data during the second transmit portion of the TDDframe.

In the present invention, the time periods corresponding to transmissionin the uplink and downlink directions can be varied dynamically in thecontext of the TDD frame. As such, at step 608, the length of the firstand second transmit portions can be adjusted based on the availabilityof data. For example, an indication that a given direction oftransmission is having a negative impact on bandwidth and latency, canlead to an adjustment in the defined TDD structure as to the uplink anddownlink transmission periods.

As would be appreciated, the particular mechanism used to initiate theadjustments can vary based on the granularity of desired in theadjustment mechanism. In one example, the adjustment can be made torespond to a particular FIFO level at a moment of time. In anotherexample, the adjustment can be made to respond to a statistical measureof bandwidth and/or latency over a particular monitored period of time.

As has been described, the principles of the present invention can beapplied to a single-pair or a multi-pair cable network. Moreover, theprinciples of the present invention can be used with twisted-paircables, coaxial cables or fiber optic cables. Significantly, theprinciples of the present invention can be combined and used withvarious modulation techniques. Additionally, the principles of thepresent invention can be designed with predefined uplink and downlinkthroughputs or can be made programmable or even adaptive.

These and other aspects of the present invention will become apparent tothose skilled in the art by a review of the preceding detaileddescription. Although a number of salient features of the presentinvention have been described above, the invention is capable of otherembodiments and of being practiced and carried out in various ways thatwould be apparent to one of ordinary skill in the art after reading thedisclosed invention, therefore the above description should not beconsidered to be exclusive of these other embodiments. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purposes of description and should not be regarded as limiting.

What is claimed is:
 1. A method in a first Ethernet physical layerdevice that is coupled to a second Ethernet physical layer device via asingle conductor pair network link, comprising: receiving transmissioncontrol during a first time period, said transmission control providingsaid first Ethernet physical layer device with use of said singleconductor pair network link for transmission to said second Ethernetphysical layer device, wherein during said first time period said secondEthernet physical layer device is prevented from transmitting over saidsingle conductor pair network link; receiving data that is transmittedby said second Ethernet physical layer device during a second timeperiod following said first time period, wherein during said second timeperiod, transmission control is relinquished to said second Ethernetphysical layer device and said first Ethernet physical layer device isprevented from transmitting over said single conductor pair networklink, wherein said first time period and said second time period alongwith two gap periods between transmission by said first and secondEthernet physical layer devices define a repeating time division duplexframe, said first time period and said second time period separated byone of said two gap periods; and lengthening at least one of said twogap periods when said first Ethernet physical layer devices has no datato send over said single conductor pair network link.
 2. The method ofclaim 1, wherein said first time period and said second time period aresubstantially equal lengths of time.
 3. The method of claim 1, whereinsaid first time period and said second time period are different lengthsof time.
 4. The method of claim 1, further comprising shortening alength of said first time period if said first Ethernet physical layerdevice has no data to send.
 5. The method of claim 1, further comprisingentering, by said first physical layer device, a low power idle modeduring if said first Ethernet physical layer device has no data to send.6. An Ethernet physical layer device for use with a single conductorpair cable, comprising: a first transmitter coupled to a singleconductor pair cable, said first transmitter responsive to atransmission control signal that determines a first assigned time periodwhen data can be transmitted by said first transmitter over said singleconductor pair cable and when data cannot be transmitted by a secondtransmitter in a second physical layer device over said single conductorpair cable; and a controller that generates said transmission controlsignal, said controller designed to cooperate with said second Ethernetphysical layer device in defining a second assigned time periodfollowing said first assigned time period when said first transmittercannot transmit data over said single conductor pair cable and saidsecond transmitter can transmit data over said single conductor paircable, wherein said controller lengthens an inter-burst gap periodbetween said first assigned time period and said second assigned timeperiod if said first Ethernet physical layer device has no data to send,wherein said first assigned time period and said second assigned timeperiod along with two gap periods, which include said inter-burst gapperiod, define a repeating time division duplex frame.
 7. The device ofclaim 6, wherein said first assigned time period and said secondassigned time period are substantially equal lengths of time.
 8. Thedevice of claim 6, wherein said first assigned time period and saidsecond assigned time period are different lengths of time.
 9. The deviceof claim 6, wherein said controller shortens a length of said firstassigned time period if said first Ethernet physical layer device has nodata to send.
 10. The device of claim 6, wherein said first physicallayer device enters a low power idle mode if said first Ethernetphysical layer device has no data to send.
 11. The device of claim 6,further comprising a first-in-first-out buffer at a media access controllayer interface, wherein a clock on a first side of saidfirst-in-first-out buffer is faster than a second side of saidfirst-in-first-out buffer.
 12. A method in a first Ethernet physicallayer device that is coupled to a second Ethernet physical layer devicevia a network link, comprising: transmitting from said first Ethernetphysical layer device to said second Ethernet physical layer deviceduring a first of two alternating time periods in which said firstEthernet physical layer device is allowed to transmit over said networklink and said second Ethernet physical layer device is not allowed totransmit over said network link; receiving at said first Ethernetphysical layer device from said second Ethernet physical layer deviceduring a second of two alternating time periods following said firstalternating time period in which said first Ethernet physical layerdevice is not allowed to transmit over said network link and said secondEthernet physical layer device is allowed to transmit over said networklink; and lengthening an inter-burst gap period between said twoalternating time periods when said first Ethernet physical layer devicehas no data to send to said second Ethernet physical layer device,wherein said first of two alternating time periods and said second oftwo alternating time periods along with two gap periods, which includesaid inter-burst gap period, define a repeating time division duplexframe.
 13. The method of claim 12, wherein said first alternating timeperiod and said second alternating time period are substantially equallengths of time.
 14. The method of claim 12, wherein said firstalternating time period and said second alternating time period aredifferent lengths of time.
 15. The method of claim 12, furthercomprising shortening a length of said first alternating time period ifsaid first Ethernet physical layer device has no data to send.
 16. Themethod of claim 12, further comprising expanding a length of said firstalternating time period if said first Ethernet physical layer device hasdata to send.
 17. The method of claim 12, further comprising entering,by said first physical layer device, a low power idle mode if said firstEthernet physical layer device has no data to send.